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Phase III of construction on the metro system in Delhi, India, will include the simultaneous use of 34 tunnel-boring machines to dig 74 tunnels, some of which will be under railroad tracks, in high groundwater areas and in rocky places. "This will be a record number of machines used at any one time in one city," writes Justin McGar.

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The $10.3 billion, 35-mile NEAT Gotthard Base Tunnel through the Swiss Alps should be operational next year. Nearly 2,000 workers have been on site of the two parallel single-track tunnels and have excavated more than 31 million tons of earth with the help of four tunnel-boring machines. When complete, it will be the world's longest rail tunnel.

The approximately $25 billion Crossrail project in London that is adding 73 miles to the city's transit system reached its halfway mark and is on track to open in 2018. The project, which includes 26 miles of new tunnels, is using eight tunnel-boring machines. Atlantic Cities provides several photos that show the progress of the project.

Mom Chung -- a 350-foot-long, 750-ton tunnel-boring machine -- began excavating a new subway tunnel in San Francisco. The machine will spend about 10 months digging a 1.5-mile tunnel as part of the $1.6 billion Central Subway project. A second TBM will bore a parallel tunnel. The project will add 1.7 miles to the Third Street light-rail system.

Due to a damaged tunnel-boring machine, the opening of the Brightwater sewage-treatment plant in King County, Wash., will be delayed again. The machine was digging a two-mile segment of a 13-mile tunnel from the sewer plant to Puget Sound. The $1.8 billion treatment plant was originally scheduled to open in 2010 but had been pushed back to 2011 before the damage to the boring machine was discovered last week.

In another sign of the growing importance of expansion in global markets, Caterpillar has acquired Lovat Inc., a manufacturer of tunnel-boring machines with operations in Canada, China and the U.K. Financial terms were not disclosed by either company.